New immobilized chiral Mn(III)salen complexes on pyridine N-oxide-modified MCM-41 as effective catalysts for epoxidation of nonfunctionalized alkenes

摘要

We prepared new chiral Mn(III)salen complexes 1'-4'immobilized on pyridine N-oxide-modified MCM-41 through the axial coordination.Epoxidation of styrene and 4-chlorostyrene with the use of these complexes as catalysts in the presence of NaOCl was found to proceed enantioselectively(ee,62-69%)at 0 deg C in 8-12 h,which is a significantly higher enantioselectivity than that observed for their homogeneous counterparts(ee,36-51%).These catalysts were also effective for the relatively bulkier alkenes,such as indene and 2,2-dimethylchromene,and have shown a reactivity(82-98%)and an enantioselectivity(69-92%)similar to those observed for their homogeneous system.The catalysts could be recycled several times without loss of performance.